Wilson Audio WATT/Puppy System 5 loudspeaker Measurements

Sidebar 3: Measurements

Coupled with a very high sensitivity—calculated at 91dB/2.83V/m (B-weighted)—the impedance of the Series 5 WATT by itself (fig.1) is definitely kinder on amplifiers than the earlier versions. Its minimum value is 5.2 ohms in the lower midrange, and the phase angle is moderately low above this region. The WATT's reflex-port tuning frequency is revealed by the impedance dip between 35Hz and 50Hz, though the high values of the impedance peaks either side of this "saddle" have implications for the crossover to the Puppy, as will be seen later. The two wrinkles in the fig.1 traces at 15.5kHz and 23kHz indicate the presence of resonances in the tweeter's output at those frequencies.

The Puppy, on the other hand, is a demanding load, its impedance (fig.2) reaching a current-hungry 2.4 ohms in the upper bass, although this will be moderated by the relatively innocuous phase angle in the same region. The rise in impedance above 100Hz is due to the low-pass crossover; the low port tuning is revealed by the magnitude saddle between 20Hz and 40Hz.

When the WATT is combined with the Puppy, the current demands of the woofer are imposed on those of the more benign monitor to produce the impedance characteristic shown in fig.3. Though it is overall a demanding load, the relative change in magnitude is mild. In addition, with a tube amplifier having a moderately high source impedance, the magnitude dip in the upper bass will usefully pull down the overall energy in this region.

The trace on the right of fig.4 shows the quasi-anechoic response of the WATT 5 by itself on an axis level with the top of its woofer. This is where I found it to measure flattest, and is 36" from the floor when the WATT is sitting on the top of the Puppy—a typical listening height for someone sitting in a typical chair (not a director's chair). The response of the WATT in free space is inherently shelved-down below the upper midrange, though this region will be reinforced by the boundary effect when the speaker is on top of the Puppy. The same would be true if the WATT were used on top of a mixing console.

The response is very smooth through the treble; only the two peaks in the upper octaves coincident with the impedance wrinkles are noticeable. In my own auditioning, I could just hear a slight emphasis of video-monitor line whistles due to the lower peak, but its effect was inaudible on music. Overall, I would expect the WATT's measured response to correlate with a sound that was smooth-balanced but very revealing of recorded detail.

To the left of fig.4 are shown three traces representing the responses of the woofer and port, both measured in the nearfield, and their complex sum. The latter is the top trace and reveals the WATT to extend down to about 55Hz without the Puppy, though the lack of lower-midrange energy makes the balance lean.

Fig.5 shows how the WATT's response changes to the sides. There is more top-octave energy apparent between 5 degrees and 25 degrees off-axis, suggesting that the user can use toe-in to optimally balance the speaker's high-treble balance. In very bare-furnished rooms, however, the speaker might sound a little "wiry." Throughout the rest of the audioband, the WATT's dispersion is very even, something that always correlates with well-defined stereo imaging, in my experience.